Optical Concentrator

ABSTRACT

Apparatus for concentrating light rays arriving from at least one opening onto a receiver, individual beams of the light rays each arriving at the apparatus substantially collimated, the apparatus including a respective Fresnel lens assembly for each opening, the Fresnel lens assembly including a first Fresnel lens, and a second Fresnel lens, the first Fresnel lens being located between the opening and the receiver, the second Fresnel lens being located between the first Fresnel lens and the receiver, the first Fresnel lens collimating the light rays arriving from the opening, the second Fresnel lens converging the collimated light rays onto the receiver, the opening being located in front of the Fresnel lens assembly, on the focal plane of the first Fresnel lens, centered on the focal point of the first Fresnel lens, and the receiver being located behind the Fresnel lens assembly, on the focal point of the second Fresnel lens.

FIELD OF THE DISCLOSED TECHNIQUE

The disclosed technique relates to optics in general, and to methods andsystems for concentrating light, in particular.

BACKGROUND OF THE DISCLOSED TECHNIQUE

The need to concentrate light is relevant in many technologicalapplications. One such application is concentrating incoming light raysfrom a light source onto a photodetector. Such a photodetector may bedetecting the wavelength of incoming light rays, its intensity, orvarious other properties or signals carried by incoming light rays.Photodetectors come in various sizes with regards to the size of theiractive detecting surface. Their price increases significantly with anincrease in their active detecting surface. A photodetector, with anactive detector surface in the square centimeter range, can cost manytimes the amount of a similar photodetector, with an active detectorsurface in the square millimeter range. It is therefore cost effectiveto be able to concentrate incoming light onto ever smallerphotodetectors. Currently, optical systems exist which can achieve thegoal of concentrating incoming light rays onto small photodetectors. Theoptical systems currently used to concentrate incoming light rays areusually either large, bulky or not cost effective. As such, they are notwell suited to be used in cases where light concentration onto smalldetectors is required and the physical size of such optical systemsneeds to be small.

U.S. Pat. No. 5,604,607 issued to Mirzaoff, and entitled “Lightconcentrator system” is directed to a system for collecting andconcentrating electromagnetic radiation. The system includes aphotosensitive medium for capturing light and a planar array locatedproximate to the photosensitive medium for guiding the light into thephotosensitive medium. The planar array includes a plurality ofconcentrator elements. The concentrator elements each have a circularinput and a circular output opening, and a hyperbolic cross section.Between each input and output opening is a reflective inner wall. Thereflective inner wall functions to guide and concentrate radiant energyor light impinging upon an input opening through the concentratorelement to an output opening towards the photosensitive medium.

U.S. Pat. No. 6,541,694 issued to Winston et al., and entitled“Nonimaging light concentrator with uniform irradiance” is directed to anonimaging light concentrator system and nonimaging optical mixerdesigns that produce uniform flux for use with photovoltaic dishconcentrators. The system includes a primary collector of light, such asa reflector dish, for producing highly concentrated light flux. Thesystem further includes an optical mixer located near the focal zone ofthe primary collector of light. The optical mixer includes a transparententrance aperture and a transparent exit aperture. The optical mixerfurther includes an internally reflective housing for substantiallytotal internal reflection of light. An array of photovoltaic cells islocated near the transparent exit aperture.

The system works as follows. Light entering the system is collected bythe primary collector of light and directed towards its focal zone. Atthe focal zone, the light enters an optical mixer. Light inside theoptical mixer is provided to the array of photovoltaic cells bysubstantial total internal reflection inside the optical mixer.Substantial total internal reflection provides for uniform light flux onthe array of photovoltaic cells.

U.S. Pat. No. 6,302,100 issued to Vandenberg, and entitled “System forcollimating and concentrating direct and diffused radiation” is directedto a system and a method for collimating light energy falling randomlyfrom a plurality of directions onto a fixed positioned thin flatsurface. The system includes a collimator for collimating incidentlight, a lens for concentrating light collimated by the collimator, alight funnel for further concentrating light concentrated by the lens,and a receiver. The collimated light is concentrated by an assembly ofconverging and diverging prismatic slabs and optical means towards thelight funnel. Each prism slab's longitudinal axis is parallel to theshortest side of the collector. Each diverging prism has a first side incontact with a converging prism, and a second side in contact withanother converging prism. The index of refraction of the convergingprisms differs from the index of refraction of the diverging prisms.

SUMMARY OF THE DISCLOSED TECHNIQUE

It is an object of the disclosed technique to provide a novel method andsystem for optically concentrating light rays using two Fresnel lenses.

In accordance with the disclosed technique, there is thus provided anapparatus for concentrating light rays arriving from at least oneopening onto a receiver, wherein the individual beams of the light rayseach arrive at the apparatus substantially collimated. The apparatusincludes a respective Fresnel lens assembly for each opening. EachFresnel lens assembly includes a first Fresnel lens and a second Fresnellens. The first Fresnel lens is located between the opening and thereceiver. The second Fresnel lens is located between the first Fresnellens and the receiver. The first Fresnel lens collimates the light raysarriving from the opening, and the second Fresnel lens converges thecollimated light rays onto the receiver. The opening is located in frontof the Fresnel lens assembly, on the focal plane of the first Fresnellens, centered on the focal point of the first Fresnel lens. Thereceiver is located behind the Fresnel lens assembly, on the focal pointof the second Fresnel lens.

According to another aspect of the disclosed technique, there is thusprovided an apparatus for concentrating light rays arriving from atleast one opening onto a receiver, wherein the individual beams of thelight rays each arrive at the apparatus substantially collimated. Theapparatus includes a respective lens assembly for each opening. Eachlens assembly includes a first lens and a second lens. The first lens islocated between the opening and the receiver. The second lens is locatedbetween the first lens and the receiver. The first lens collimates thelight rays arriving from the opening. The second lens converges thecollimated light rays onto the receiver. The opening is located in frontof the lens assembly, on the focal plane of the first lens, centered onthe focal point of the first lens. The receiver is located behind thelens assembly, on the focal point of the second lens.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed technique will be understood and appreciated more fullyfrom the following detailed description taken in conjunction with thedrawings in which:

FIG. 1A is a schematic diagram of the prior art illustrating thecollimating properties of convex lenses and Fresnel lenses.

FIG. 1B is a schematic diagram illustrating the converging properties ofconvex and Fresnel lenses;

FIG. 2 is a schematic diagram of a system, constructed and operative inaccordance with an embodiment of the disclosed technique; and

FIG. 3 is a schematic diagram of another system, constructed andoperative in accordance with an embodiment of the disclosed technique.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The disclosed technique overcomes the disadvantages of the prior art byproviding an optical concentrator comprising two Fresnel lenses. OneFresnel lens is used to collimate incoming light rays, whereas the otherFresnel lens is used to concentrate the incoming light rays onto a smallphotodetector. The disclosed technique provides a product which islightweight, compact, and cost effective.

Fresnel lenses produce the same optical effects of conventional lenses,be it concentrating light, collimating light, or dispersing light, for afraction of the weight, volume and width of conventional lenses. This isdue to their unique design. Reference is now made to FIG. 1A, which is aschematic diagram illustrating the collimating properties of a convexlens and a Fresnel lens. Convex lens 20 has a property whereby lightrays 21 passing through its surface are collimated provided such lightrays pass through point 24, an imaginary point known as the focal point.In fact, any light ray passing through line 26, an imaginary line knownas the focal plane, will be collimated by convex lens 20. This propertyis due to the refractive nature of light rays passing through differentmedia. The distance from focal plane 26 to convex lens 20 is known asthe focal length and is specific for the particular curvature of convexlens 20. Fresnel lens 22, just like convex lens 20, has the sameproperty whereby light rays 21 passing through its surface arecollimated, provided such light rays pass through its focal point 28 orits focal plane 30.

Reference is now made to FIG. 1B, which is a schematic diagramillustrating the converging properties of a convex lens and a Fresnellens. Convex lens 20 has a property whereby collimated light 32 passingthrough its surface can be converged onto its focal point 24. Thisproperty is due to the refractive nature of light rays passing throughdifferent media. Fresnel lens 22, just like convex lens 20, has the sameproperty whereby collimated light 32 passing through its surface isconverged onto its focal point 28.

Reference is now made to FIG. 2, which is a schematic diagram of asystem, generally referenced 100, constructed and operative inaccordance with an embodiment of the disclosed technique. System 100includes opening 102, first Fresnel lens 104, second Fresnel lens 106,and photodetector 108. System 100 may be encapsulated in closedstructure 114 to prevent ambient light or other external light sourcesfrom entering it. Opening 102 is located on the focal plane of firstFresnel lens 104, centered along optical axis 112 of first Fresnel lens104 and second Fresnel lens 106. Opening 102 is located in front offirst Fresnel lens 104. Optical axis 112 passes through the focal pointsof both Fresnel lenses. Opening 102 can vary in size. If opening 102 islarger than the diameter of Fresnel lenses 104 and 106, some of thelight entering system 100, via opening 102, may not be concentrated onphotodetector 108. Side 114 of first Fresnel lens 104 is ridged, whereasside 116 of first Fresnel lens 104 is flat. Fresnel lenses can bereferred to as ridged lenses as their unique design gives them theappearance of having ridges. First Fresnel lens 104 has its ridged side114 facing opening 102. First Fresnel lens 104 and second Fresnel lens106 are substantially similar in size. Second Fresnel lens 106 islocated behind first Fresnel lens 104, centered on optical axis 112 suchthat optical axis 112 passes through its focal point. Side 120 of secondFresnel lens 106 is ridged, whereas side 118 of second Fresnel lens 106is flat. Second Fresnel lens 106 has its flat side 118 facing opening102. In an embodiment of the disclosed technique, second Fresnel lens106 and first Fresnel lens 104 are fit together by joining side 116 offirst Fresnel lens 104 to side 118 of second Fresnel lens 106. Inanother embodiment of the disclosed technique, first Fresnel lens 104and second Fresnel lens 106 are located a distance apart from oneanother. In a further embodiment of the disclosed technique, firstFresnel lens 104 can have its flat side 116 facing opening 102. Inanother embodiment of the disclosed technique second Fresnel lens 106can have its ridged side 120 facing opening 102. Photodetector 108 islocated on the focal plane of second Fresnel lens 106, centered onoptical axis 112. Photodetector 108 is located behind second Fresnellens 106. This means that photodetector 108 is located on the focalpoint of second Fresnel lens 106. Photodetector 108 is significantlysmaller than the size of opening 102.

System 100 works in the following generalized manner. Light rays 110Aarrive at system 100 from multiple directions. Incoming, light rays110A, to be concentrated on photodetector 108, pass through opening 102.Since the size of opening 102 is, in general, much smaller than thedistance between system 100 and the source of light rays 110A, eachindividual beam of light passing through opening 102 will pass therethrough as a substantially collimated beam of light. Opening 102 is theonly way for incoming light rays to fall incident on Fresnel lenses 104and 106 because system 100 may be completely encapsulated within closedstructure 114. Since opening 102 is smaller than or equal to thediameter of Fresnel lenses 104 and 106, and since opening 102 lies onthe focal plane of first Fresnel lens 104, any light rays passingthrough opening 102 and falling incident on first Fresnel lens 104 willbecome substantially collimated, or substantially parallel with oneanother, after passing through first Fresnel lens 104. Once incominglight rays 110A pass through first Fresnel lens 104, they emerges assubstantially collimated light rays 110B due to the specific location ofopening 102 vis-a-vis first Fresnel lens 104. Substantially collimatedlight rays 110B then fall incident on second Fresnel lens 106. Since thelight rays falling incident on second Fresnel lens 106 are substantiallycollimated, they will pass through second Fresnel lens 106 and thenconverge onto the focal point of second Fresnel lens 106. Sincephotodetector 108 is located on the focal point of second Fresnel lens106, convergent light rays 110C exiting second Fresnel lens 106 will beconcentrated on photodetector 108.

In general, there is no restriction on the distance between firstFresnel lens 104 and second Fresnel lens 106, although due to the ridgednature of first Fresnel lens 104, some of substantially collimated lightrays 110B may disperse slightly once they pass through first Fresnellens 104. The amount of dispersion, in terms of distance from the endsof second Fresnel lens 106, depends on the distance between the twoFresnel lenses. As the distance between the two Fresnel lensesincreases, the amount of dispersion, in terms of distance from the endsof second Fresnel lens 106, also increases. If the amount of dispersionis significant, then the diameter of second Fresnel lens 106 needs to beincreased accordingly to converge the dispersed rays that pass throughfirst Fresnel lens 104 onto photodetector 108.

It is noted that first Fresnel lens 104 and second Fresnel lens 106 caneach be replaced by a cylindrical Fresnel lens. It is also noted thatfirst Fresnel lens 104 and second Fresnel lens 106 can be replaced by adouble-sided Fresnel lens. It is further noted that first Fresnel lens104 and second Fresnel lens 106 can each be replaced by a sphericallens, a cylindrical lens, or a regular lens.

Reference is now made to FIG. 3, which is a schematic diagram of anothersystem, generally referenced 140, constructed and operative inaccordance with an embodiment of the disclosed technique. System 140includes three Fresnel lens sets which are each substantially similar tosystem 100 (FIG. 2). System 140 includes openings 142 _(A), 142 _(B) and142 _(C), first Fresnel lenses 144 _(A), 144 _(B) and 144 _(C), secondFresnel lenses 146 _(A), 146 _(B) and 146 _(C), and photodetector 148.One side of each of first Fresnel lenses 144 _(A), 144 _(B) and 144 _(c)is ridged, whereas the other side of each of first Fresnel lenses 144_(A), 144 _(B) and 144 _(C) is flat. One side of each of second Fresnellenses 146 _(A), 146 _(B) and 146 _(C) is ridged, whereas the other sideof each of second Fresnel lenses 146 _(A), 146 _(B) and 146 _(C) isflat. First Fresnel lenses 144 _(A), ¹⁴⁴B and 1 ⁴⁴c, and second Fresnellenses 146 _(A), 146 _(B) and 146 _(C), are substantially similar insize.

Opening 142 _(A) is located on the focal plane of first Fresnel lens 144_(A), centered along optical axis 152 _(A) of first Fresnel lens 144_(A) and second Fresnel lens 146 _(A). Opening 142 _(A) is located infront of first Fresnel lens 144 _(A). Optical axis 152 _(A) passesthrough the focal points of both Fresnel lenses. Second Fresnel lens 146_(A)is located behind first Fresnel lens 144 _(A), centered on opticalaxis 152 _(A) such that optical axis 152 _(A) passes through its focalpoint. Opening 142 _(B) is located on the focal plane of first Fresnellens 144 _(B), centered along optical axis 152 _(B) of first Fresnellens 144 _(B) and second Fresnel lens 146 _(B). Opening 142 _(B) islocated in front of first Fresnel lens 144 _(B). Optical axis 152 _(B)passes through the focal points of both Fresnel lenses. Second Fresnellens 146 _(B) is located behind first Fresnel lens 144 _(B), centered onoptical axis 152 _(B) such that optical axis 152 _(B) passes through itsfocal point. Opening 142 _(C) is located on the focal plane of firstFresnel lens 144 _(c), centered along optical axis 152 _(C) of firstFresnel lens 144 _(c) and second Fresnel lens 146 _(C). Opening 142 _(C)is located in front of first Fresnel lens 144 _(c). Optical axis 152_(C) passes through the focal points of both Fresnel lenses. SecondFresnel lens 146 _(C) is located behind first Fresnel lens 144 _(C),centered on optical axis 152 _(C) such that optical axis 152 _(C) passesthrough its focal point.

Photodetector 148 is located on the intersection of the focal planes ofsecond Fresnel lenses 146 _(A), 146 _(B) and 146 _(C). Photodetector 148is located behind second Fresnel lenses 146 _(A), 146 _(B) and 146 _(C).This means that photodetector 148 is located on the focal points ofsecond Fresnel lenses 146 _(A), 146 _(B) and 146 _(C). Second Fresnellenses 146 _(A), 146 _(B) and 146 _(C) are configured such that theirrespective focal points all coincide. Photodetector 148 is significantlysmaller than the size of openings 142 _(A), 142 _(B) and 142 _(C).Openings 142 _(A), 142 _(B) and 142 _(C) can vary in size. If theopenings are larger than the diameter of the Fresnel lenses, some of thelight entering system 140, via opening 142 _(A), 142 _(B) and 142 _(C)may not be concentrated on photodetector 148. In an embodiment of thedisclosed technique, second Fresnel lenses 146 _(A), 146 _(B) and 146_(C) are each respectively fit together to first Fresnel lenses 144_(A), 144 _(B) and 144 _(C) by respectively joining the flat side ofeach of first Fresnel lenses 144 _(A), 144 _(B) and 144 _(C) to therespective flat side of each of second Fresnel lenses 146 _(A), 146 _(B)and 146 _(C).

Each Fresnel lens set and opening (for example opening 142 _(A), firstFresnel lens 144 _(A) and second Fresnel lens 146 _(A)) is configured toreceive light rays, for example light rays 150 _(A), 150 _(B) and 150_(C), coming from different directions. It is noted that each individualbeam of light, in each of light rays 150 _(A), 150 _(B) and 150 _(C),arrives at system 140 substantially collimated. Each individual beam oflight arrives at system 140 substantially collimated since the size ofopenings 142 _(A), 142 _(B) and 142 _(C) are, in general, much smallerthan the distance between system 140 and the source of light rays 150_(A), 150 _(B) and 150 _(C). The location and orientation of eachFresnel lens set and opening, with respect to one another, is such thatphotodetector 148 is simultaneously located at the focal point of eachsecond Fresnel lens of each Fresnel lens set. In another embodiment ofthe disclosed, a plurality of Fresnel lens sets and openings areconfigured to receive light rays coming from different directions. Thelocation and orientation of each Fresnel lens set and opening, withrespect to one another, is such that photodetector 148 is simultaneouslylocated at the focal point of each second Fresnel lens of each Fresnellens set. System 140 allows light rays coming from a plurality ofdirections to be concentrated onto a single photodetector.

It will be appreciated by persons skilled in the art that the disclosedtechnique is not limited to what has been particularly shown anddescribed hereinabove. Rather the scope of the disclosed technique isdefined only by the claims, which follow.

1. Apparatus, for concentrating light rays arriving from at least oneopening onto a receiver, the distance between the source of said lightrays and said apparatus being substantially larger than the size of saidopening, individual beams of said light rays thereby each arriving atsaid apparatus substantially collimated, comprising: a respectiveFresnel lens assembly for each said at least one opening, said at leastone respective Fresnel lens assembly including: a first Fresnel lens,located between a respective one of said at least one opening and saidreceiver, for making parallel with an optical axis of said first Fresnellens, said light rays arriving from said respective one of said at leastone opening; and a second Fresnel lens, located between said firstFresnel lens and said receiver, for converging said parallel light raysonto said receiver, wherein each said at least one opening is located infront of said respective Fresnel lens assembly, on the focal plane ofsaid respective first Fresnel lens, centered on the focal point of saidrespective first Fresnel lens, wherein said receiver is located behindeach said at least one respective Fresnel lens assembly, on the focalpoint of the respective said second Fresnel lens.
 2. The apparatusaccording to claim 1, wherein, for each said respective Fresnel lensassembly, the distance from said respective one of said at least oneopening to said receiver is approximate to the accumulated distance ofthe focal length of said respective first Fresnel lens, the focal lengthof said respective second Fresnel lens and the space between saidrespective first Fresnel lens and said respective second Fresnel lens.3. The apparatus according to claim 2, wherein said respective firstFresnel lens and said respective second Fresnel lens each include aridged side and a flat side, wherein said respective first Fresnel lenshas its ridged side facing said respective one of said at least oneopening and its flat side facing said respective second Fresnel lens,and wherein said respective second Fresnel lens has its flat side facingsaid respective first Fresnel lens and its ridged side facing saidreceiver.
 4. The apparatus according to claim 3, wherein said respectiveFresnel lenses are substantially similar in size.
 5. The apparatusaccording to claim 2, wherein said space equals zero.
 6. The apparatusaccording to claim 3, wherein said respective Fresnel lenses are joinedtogether into a single optical element.
 7. The apparatus according toclaim 2, wherein, for each said respective Fresnel lens assembly, saidrespective one of said at least one opening is substantially equal insize, or smaller in size, than a diameter of said respective firstFresnel lens and said respective second Fresnel lens.
 8. The apparatusaccording to claim 1, further comprising a closed structure forpreventing ambient light from entering said apparatus, wherein said atleast one opening is located on said closed structure, and said closedstructure encapsulates said respective Fresnel lens assembly and saidreceiver.
 9. The apparatus according to claim 1, wherein at least one ofsaid first Fresnel lens and said second Fresnel lens, is selected fromthe group consisting of: Fresnel lens; cylindrical Fresnel lens; anddouble-sided Fresnel lens.
 10. Apparatus, for concentrating light raysarriving from at least one opening onto a receiver, the distance betweenthe source of said light rays and said apparatus being substantiallylarger than the size of said opening, individual beams of said lightrays thereby each arriving at said apparatus substantially collimated,the apparatus comprising: a respective lens assembly for each said atleast one opening, said at least one respective lens assembly including:a first lens, located between a respective one of said at least oneopening and said receiver, for making parallel with an optical axis ofsaid first lens said light rays arriving from said respective one ofsaid at least one opening; and a second lens, located between said firstlens and said receiver, for converging said parallel light rays ontosaid receiver, wherein each said at least one opening is located infront of said respective lens assembly, on the focal plane of saidrespective first lens, centered on the focal point of said respectivefirst lens, wherein said receiver is located behind each said at leastone respective lens assembly, on the focal point of the respective saidsecond lens.
 11. The apparatus according to claim 10, wherein, for eachsaid respective lens assembly, the distance from said respective one ofsaid at least one opening to said receiver is approximate to theaccumulated distance of the focal length of said respective first lens,the focal length of said respective second lens and the space betweensaid respective first lens and said respective second lens.
 12. Theapparatus according to claim 11, wherein said respective first lens andsaid respective second lens each include a ridged side and a flat side,wherein said respective first lens has its ridged side facing saidrespective one of said at least one opening and its flat side facingsaid respective second lens, and wherein said respective second lens hasits flat side facing said respective first lens and its ridged sidefacing said receiver.
 13. The apparatus according to claim 12, whereinsaid respective lenses are substantially similar in size.
 14. Theapparatus according to claim 11, wherein said space equals zero.
 15. Theapparatus according to claim 12, wherein said respective lenses arejoined together into a single optical element.
 16. The apparatusaccording to claim 11, wherein, for each said respective lens assembly,said respective one of said at least one opening is substantially equalin size, or smaller in size, than a diameter of said respective firstlens and said respective second lens.
 17. The apparatus according toclaim 10, further comprising a closed structure for preventing ambientlight from entering said apparatus, wherein said at least one opening islocated on said closed structure, and said closed structure encapsulatessaid respective lens assembly and said receiver.
 18. The apparatusaccording to claim 10, wherein at least one of said first lens and saidsecond lens is selected from the group consisting of: cylindricallenses; and regular lenses.
 19. The apparatuses according to any of theclaims 1-18 substantially as described hereinabove or as illustrated inany of the drawings.